Polygon.io API
Market data platform providing real-time and historical stock, options, forex, and crypto price data via REST and WebSocket with SIP consolidated tape access and a generous free tier for delayed data.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Single API key with no scope granularity — key compromise exposes all data access. No IP allowlisting. Key should be stored as a secret and rotated regularly. Data is market data only (no PII or financial account access).
⚡ Reliability
Best When
Your agent needs affordable, developer-friendly access to real-time or historical US equity, options, or crypto market data with solid WebSocket streaming.
Avoid When
You need full-depth level 2 order book data or institutional-grade direct exchange feeds with sub-millisecond guarantees.
Use Cases
- • Stream real-time NBBO quotes and last sale data for equities via WebSocket for signal-generating trading agents
- • Query multi-year historical OHLCV candlestick data for backtesting and ML feature engineering pipelines
- • Fetch options chain snapshots including Greeks, open interest, and IV for options strategy agents
- • Subscribe to real-time forex mid-prices across 100+ currency pairs for FX monitoring or hedging agents
- • Use the aggregates endpoint to pre-compute VWAP, daily highs/lows, and volume statistics across a watchlist
Not For
- • Order execution — Polygon is market data only; pair with a brokerage API (Alpaca, Interactive Brokers) for trading
- • Corporate actions, fundamentals, or earnings data — use a dedicated data provider like Intrinio or Quandl
- • Tick-level institutional data requiring co-located feeds — Polygon distributes via cloud, not colocation
Interface
Authentication
Single API key passed as query parameter or Authorization header. Key permissions tied to subscription tier — lower tiers return 403 on premium endpoints rather than indicating the required tier.
Pricing
Free tier is useful for development and testing. Real-time NBBO (SIP) requires Developer plan or higher. Options Greeks require Advanced plan.
Agent Metadata
Known Gotchas
- ⚠ Free tier returns 15-minute delayed data with no warning in the response — agents may mistake delayed data for real-time without checking the subscription tier
- ⚠ WebSocket connections require subscribing to individual ticker symbols; wildcard subscriptions (T.*) count against connection limits and can exhaust rate budgets rapidly
- ⚠ Historical aggregate endpoints return results in ascending time order by default but sort direction is configurable — agents must be explicit to avoid reversed series
- ⚠ Ticker symbol format differs between asset classes (stocks use 'AAPL', options use 'O:AAPL251219C00150000', crypto uses 'X:BTCUSD') — agents must normalize symbols before cross-asset queries
- ⚠ The /v2/last/nbbo endpoint returns the most recent NBBO quote but may be stale outside market hours; agents must check the timestamp before using the value in time-sensitive logic
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Polygon.io API.
Scores are editorial opinions as of 2026-03-06.